This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The bacterium Staphylococcus aureus is a serious human pathogen and a public health concern in both community and clinical settings. Bacterial resistance to antimicrobial agents, however, reduces chemotherapeutic effectiveness against infectious diseases caused by S. aureus, and in particular, multi-drug resistant strains of this bacterium. Thus, knowledge of such resistance mechanisms would be of clinical utility in the efforts to control the mechanisms that confer resistance, thus restoring the usefulness of chemotherapeutics. The long term objectives of the experiments proposed in this project application are to enhance our understanding of the functional roles of the multidrug efflux pump operon and its transcriptional regulatory system in clinical isolates of methicillin resistant S. aureus (MRSA) and vancomycin intermediate S. aureus (VISA). The central hypotheses are that farABC-encoded efflux pumps mediate resistance to fusidic acid and ethidium, provide scaffolding for clinical resistance to arise, and that yycFG elements control transcription of these pump genes, thus contributing to antimicrobial drug resistance. The rationale for these hypotheses is that once the relationships are known between the multidrug efflux pumps and their transcriptional control systems, then insight will be gained regarding Staphylococcal resistance mechanisms to multiple antimicrobial agents. The expected outcomes are that the training efforts will be facilitated for undergraduates and graduates plus postdoctoral fellows. Physiological studies with transcriptional regulation will provide molecular insight into important systems for bacterial resistance to antimicrobial agents in a serious human pathogen that is a public health concern in both community and clinical settings.